Glass



Patented Sept. 16, 1924...

CHARLES A. KRAUS, WORCESTER, MASSACHUSETTS.

GLASS.

No Drawing.

To all whom it may concern:

Be it known that I, CHARLES A. KnAUs, a citizen of the United States, residing at Worcester, in the county of Worcester and State of Massachusetts, have invented "certain new and useful Improvements in Glass,

' of which the following is a full, clear, and

exact description.

My invention relates to improvements in the composition of glasses and is addressed in particular to glasses having a low coefficient of expansion and having other properties which render them commercially useful.

In patent application Serial No. 404,863, filed August 20, 1920, I have described a number of glasses having a low coefficient of expansion. As I showed there, the Hovestadt numbers which have hereto-fore been employed in predetermining the coefficient of expansion of a given composition are largely in error when applied to glasses hav ing a low coeflicient of expansion. I have found further that the partial coefficients employed in calculating the coeflicient of expansion of a given composition are governed not alone by the magnitude of the coefficient of expansion of the composition, but depend also upon the nature of the constituent oxides which go to make up the the relation between the coefficient of expansion and the composition-is not a linear one, but is in general a function of the amounts of the substances present.

In general, a gla$ in order to be commercially useful should have a low coefficient of expansion, should beresistant to theaction of various solvent agents and should have a low softenin temperature. In addition, it is desirable and often necessary that the substances entering into the composition shall be readily obtainable upon the market at a price which makes .it possible to manufacture the lass at a low cost. In the above-mention .patent application I have described various compositions having a low coeflicient of expansion, having a high resistance'to solvent action, and having a relatively low softening temperature. My

to producin a glass having these desirable readily and at a-low cost.

composition. Furthermore, it appears that A tial coe present invention is in particular addressed Application filed October 13, 1920. Serial No. 416,700.

I have found that a glass may be produced which contains as constituent substances sodium oxide (Na O), lead oxide (PbO), boric oxide (B 0 and silica (SiO Such glasses, in general, have very low coeflicients of expansion, usually below about 4.O 10' The possibility of the production of such a glass appears not to have been recognized heretofore. This is probably due to the general acceptance of the applicability of the Hovestadt numbers. For example, a glasscontaining 25 per cent of lead oxide, 11.9 per cent of boric oxide, 3.1 per cent of sodium oxide, and 60 per cent of silica would have, according to the Hovestadt numbers, a coefficient of linear expansion of approximately 5.2 10-' expansion of this glass is 3.8 10' A glass containing per cent of silica, 3.1 per cent of sodium oxide, 6.9 per cent of boric' oxide, and 40 per cent of lead oxide would, according to the Hovestadt numbers, have a coefiicient of linear expansion of 6.4, where the actual coefficient of expansion of such composition is 4.95. It is evident, therefore,

that the Hovestadt numbers are entirely unreliable and that they cannot be used in detel-mining the coefficient of expansion of proposed compositions, 'if the composition in question isone which has a low coeflicient of-expzansion. Moreover, this failure of the Hovestadt numbers is not confined to glasses having a high content of silica, a s'has been suggested by Sullivan and Taylor. In the examples above given the-content ofsilica is low, as compared with that -ofordinary The actual coeflicient of glasses, and yet the Hovestadt numbers do not hold.

Thenumbers which I have given for the partial coefiicients for the various oxides in my above-mentioned patent application hold well for glasses of the type as exemplified in the table given in that applicatlon, but

require modification when applied to compositions' containing sodium oxide and lead oxide in larger amounts. I find that while in the gresence of potassium oxide theparcient for lead oxide is approximately a value 01 2.3, in the 2.3. For glasses which do not contain too large an amount of lead oxide, for example, which contain less than 25 per cent, apar- I resence of sodium oxide the partial coefficient is smaller than tial coeflicient of'1.6 is in. good agreementmy patent application Serial No. 404,863.

A glass, however, containing the same amounts of silica, boric oxide, and lead oxide, but containing 3.1 per cent of Sodium oxide, in place of t e potassium oxide, has a coefiicien-t of 3.8 10. While it might be said that the difference in the coetiicients of these two glasses could be equally well explained by assuming that the coetlicient for sodium oxide is smaller than the value 12.0 as given in my eariler atent application, such an assumption wou ld not lead to results in agreement with the measured values in the case of glasses having lower and higher contents of lead oxide.

But, however the coefiicients may be adjusted for the purpose of accounting for the measured coeiiicient of expansion, thefaot remains, and this is an important element of my invention, that a glass containing a given amount of lead oxide in the presence of sodium oxide has a lower coefficient of expansion than a similar glass which contains potassium oxide.

I have found, moreover, that the glasses which contain sodium oxide possess certain other advantages over lasses containing potassium oxide. Thus, t e glasses which contain sodium oxide are somewhat more readily fusible; that is to say, the possess a lower softening temperature t an glasses containing a corresponding amount of .potassiuni oxide. So, also, I find that lead lasses containin sodium oxide are reduced ess readily in t e flame than are glasses containin otassium oxide.

In the ollowing table are given the compositions of various glasses which exem lify my invention, together with some 0 the more important properties of these glasses. Under the column headed a is given the measured linear coeflicient of expansion multiplied by 10 Under the column headed H is given the relative hardness factor of the various glasses referred to pyrex glass, containing substantially 7 0 per cent of silica, 20 per cent of boric oxide, 4: per cent of sodium oxide, and 6 per cent of alumina, as a standard for comparison. The method of determining the relative hardness of glasses l have described in m application for Letters'Patent above ne erred to. Under the column headed S is given the solubility of .are in general adde for determining the solubility is likewise described in the above-named patent application.

Table.

B205. PhD.

. Sloaeral in such cases by increasing the amount of sodium oxide. A low percentage of boric oxide, moreover, is often advantageous from a manufacturing point of View, since the melt is less active on the walls of the glass pot.

It will be understood that at times it is desirable to produce an opalescent glass, that is a glass which contains within the body of the mass small particles ofmaterial which ive to it a white or translucent appearance.

ince it is always necessary for commercial purposes o control the opaqueness or transparency of such a product, such glasses come within the scope of these specications.

At times it is desirable to give to a glass color in order to meet some particular requirement, for which urpose certain oxides d as it is well understood by one skilled in the art. So, also it may be desirable to add some particu ar element, as for example barium oxide, for the purpose of giving to the glass certain properties, as for example a high index of refraction. It is to be understood that the constituents which. I have given in these specifications are the essential constituents only and that other constituents may be added for particular purposes without departing from my invention.

An examination of the column headed a shows that the glasses'here described ossess a low coeficient of thermal expansion. Of the glasses containing sodium oxide, only that of glass No. 5 is greater th 450x10 and in this case the glass contains as much as 40 per cent of lead oxide.

In general the solubility of these glasses is extremely low. This is an important factor in the production of cooking utensils, chemical glassware, and the e.

The great-advantage which these glasses lld softening temperature. Glasses which have a high softening temperature are usually termed hard glasses. Under the column headed H are given the relative hardness factors in terms of that of pyrex glass, as described in the specifications above. It will be seen that all these glasses are relativel very soft.

What I claim and wish to ters Patent is:

1. A glass containing lead oxide and having a coefiicient of thermal expansion below about 4.0X10'.

2. A glass containing lead oxide and sodium oxide and having a coeflicient of expansion less than about 4.0X10

3. A glass containing lead oxide and having a coeflicient of expansion less than about 4.0)(10 and solubility less than 0.050.

4. A glass containing lead oxide, having a coefficient of expansion less than about 4.0X10" and a hardness less than 0.9.

5. A glass containing lead oxide, having a 'coeflicient of expansion less than about 4.0X10', a hardness less than 0.9 and a solubility less than 0.05.

6. A glass containing lead oxide and not more than 5 er cent of sodium oxideand having a 'coe cient of expansion less than about 4.95X10'.

- A glass containing more than 25 per secure by Letof expansion lower than about 4.95X10.

8. A glass containing less than 70 per 7 cent of silica and more than 10 per cent of lead, oxide, and having a coefiicient of expansion less than about 4.0X10'.

9. A glass containing less than 70 per cent of silica, more than 10 per cent of lead oxide, and containing also boric' oxide and alkali, and having a coeflicient of expansion less than about 40x10".

10. A lass containin' more than 10 per cent of ead oxide an less than 70 per cent of silica, and having a coeflicient of expansion below about 4.0X10', and a hardness less than-0.9.

11. A glass containing silica, boric oxide, alkali, and the oxide of lead, and having a coefiicient of expansion less than about 4.0X10

12. A glass containing silica, lead oxide, and an alkali, and having a coeflicient of expansion less than about 4.95X10"-.

13. A glass containin silica, lead oxide, and sodium oxide and aving a coeflicient of expansion less than about 4.95X10'.

14. A glass containing silica, leads oxide and an alkali, having a coeflieient of ex pansion less than about 4:.95X10 andav low softening point as compared with that if In testimony whereof 1- hereto afiix of silica.

signature.

CHARLES A. KRAU S'. 

